1. The Field of the Invention
The present invention relates generally to apparatus and methods for stabilizing, restraining, and positioning a portion of the body of a patient during a medical procedure. More specifically the present invention relates to apparatus and methods for stabilizing, restraining, and comfortably positioning a portion of the body of a patient, while improving image quality during Magnetic Resonance Imaging and Computerized Tomography scanning procedures.
2. The Background Art
Computerized Tomography (xe2x80x9cCTxe2x80x9d) scanning and Magnetic Resonance Imaging (xe2x80x9cMRIxe2x80x9d) are procedures used for obtaining unique cross sectional views of a patient""s internal anatomy, thereby aiding in diagnosis and treatment. CT scanning involves the use of many low dosage x-rays being passed through the body at different angles to produce cross sectional images of body tissue with the aid of a computer. MRI involves the use of electromagnets and short bursts of powerful magnetic fields and radio waves, rather than x-rays, being passed through the body. The bursts stimulate the hydrogen atoms in the patient""s tissue to produce a signal that a magnetic coil detects and a computer transforms into an image.
Both of these procedures require a patient""s absolute stillness in the area of the body being imaged. Patient motion is an ever-present problem for the radiologist. During the actual sequence the patient must remain absolutely motionless or the images will be blurred, often rendering them uninterpretable. This disruption in the images is known as xe2x80x9cmotion artifact.xe2x80x9d
Motion artifact is a constant problem in all MRI because this procedure requires a relatively long period of time to obtain the images. In MRI, the patient must remain motionless for multiple imaging sequences that comprise the total exam. The exam may last 30 to 60 minutes and each sequence typically takes about 4 to 9 minutes to run. While CT scanning has much shorter imaging times than MRI, there are motion considerations in patients who are unable to cooperate. Many head CT scans are performed for the acutely injured patient and for those with sudden mental status changes. Both groups of patients are compromised in their ability to hold still and would benefit from a motion-limiting device.
In either MRI or CT scans, maintaining absolute stillness can be a challenge for an otherwise healthy adult. For an adult afflicted with tremors (such as in Parkinson""s Disease), pediatric patients, patients with altered mental status from stroke or trauma, intoxicated patients, and those patients who simply fall asleep during the imaging test and are twitchy sleepers, maintaining stillness may be virtually impossible.
Patient motion can be divided into two categories: macro motion and micro motion. Macro motion occurs on the scale of centimeters and results in the body part of interest actually moving out of the field of view. This results in images that do not include the body part of interest. The patient then has to be xe2x80x9cre-scoutedxe2x80x9d and the sequence repeated once the body part has been re-localized. This results in a loss of about 5 to 7 minutes. Micro motion occurs on a scale of millimeters and may be the result of a patient tremor, cardiac pulsation, breathing, patient restlessness, or patient discomfort resulting in unconscious twitching and shifting. This micro motion results in blurred images, which also have to be repeated. Fortunately, the patient does not need to be re-localized for these repeat sequences.
Radiologists expend extensive effort to combat patient movement. The current practice for combating patient movement involves the use of make-shift restraints from foam pads, pillows, and/or towels. Patients are brought into the MRI machine (or CT scanner) and positioned with their limb or head in the appropriate coil or imaging device. The foam pads, pillows and/or towels are then used with tape and straps to stabilize the body part and obtain a comfortable position. This positioning often takes several minutes and is fraught with poor success. Patient motion occurs because the pads, pillows, etc., do not create a custom fit and are limited in their restraining ability. Likewise, the lack of custom fit cannot create or maintain patient comfort. There are inevitable pressure points that result from a fold in the pillow, the corner or seam of a pad, and/or the edge of the coil or imaging device. The patient may have started the exam feeling quite comfortable, but after 20-30 minutes, an intolerable pressure point develops and the patient is ultimately compelled to shift his body. This even occurs in the normally conscious and cooperative patient despite his best efforts to hold still.
Fundamentally, the foam pad/pillow system is neither comfortable nor does it provide an adequate level of restraint. In addition, foam pads and pillows inherently lack the custom fit or restraint of the limb necessary to avoid all micro and macro motion.
Motion degradation leads to a significant number of non-diagnostic studies and also to considerable waste of resources. MRI time is expensive; rescanning a 5 minute sequence costs about $50 in lost magnet time. If only one sequence is rescanned on every patient on a busy MRI scanner performing 25 exams per day, roughly 125 minutes of imaging time is lost representing about 4 patient slots of at least about $1400 in technical income and roughly $400 in professional income. Clearly, motion can have a significant impact on MRI productivity. Furthermore, the delays related to patient motion will make all the subsequent patients wait, leading to customer dissatisfaction. There are approximately 6000 MR scanners in the United States. Typically, each scanner performs 5-10 brain and/or extremity examinations daily that would benefit from improved restraint and comfort.
While the time penalty for motion on a CT scanner is less severe, many of the studies on acutely head injured patients are impossible to obtain due to motion. There are approximately 6000 CT scanners in the USA. Roughly 5 head CT exams are performed each day per scanner yielding 30,000 studies. Perhaps, half of these are in patients with altered mental state, and therefore high risk of motion. Often times these scans have to be repeated to obtain better images.
In view of the foregoing, it is a primary object of the present invention to provide methods and apparatus for comfortably positioning a patient in an MRI or CT scanner or other imaging device (hereinafter xe2x80x9cMRIxe2x80x9d).
It is another object of the present invention to provide methods and apparatus for comfortably positioning a patient""s head or limb in an MRI.
It is a further object of the present invention to provide methods and apparatus for providing a custom fit of a patient""s head or limb in an MRI.
It is another object of the present invention to provide methods and apparatus for providing optimal placement of a patient""s head or limb in an MRI.
Still another object of the present invention is to provide methods and apparatus having a level of restraint that substantially diminishes or precludes all micro and macro motion of a patient""s head or limb in an MRI.
Yet another object of the present invention is to provide methods and apparatus for a low cost, disposable restraining device, which will decrease the time to set up a patient for scanning, thereby further improving MRI productivity.
Yet another object is to provide a custom fit for the flex/wrap or surface coils used in some MRI imaging that comfortably secures and restrains the body part and achieves rigid, yet comfortable fixation of the coil to the patient and to the MRI.
It is another object of the present invention to provide methods and apparatus for improving the intrinsic imaging quality of the MRI due to, for example, improved field homogeneity, signal to noise ratio, fat saturation, etc.
Still another object of the present invention is to provide methods and apparatus for improving patient tolerance of the imaging procedure by improving patient comfort.
These and other objects and advantages of the invention will be better understood by reference to the detailed description or will be appreciated by the practice of the invention. Consistent with the foregoing objects, and in accordance with the embodiments as embodied and broadly described herein, the restraining apparatus of the present invention will limit motion on the macro and micro scales by providing a custom fit, while also improving patient comfort. The restraining apparatus preferably comprises a disposable component, including a castable sleeve and, in a preferred embodiment, an expandable sleeve, both of which are used to fix the patient into the coil. The castable sleeve encircles the limb of a patient, and is filled with a quickly casting material. The casting material is MRI compatible, safe and rapid setting, which will decrease the time to set up a patient for scanning, thereby further improving MRI productivity. In addition, the casting material may augment the quality of the image, such as by improving the signal to noise ratio, the field homogeneity, and the fat saturation. The resulting cast sleeve is also MRI compatible and provides a comfortable custom fit for the patient that helps restrain the patient in the imaging device.
In one preferred embodiment, the expandable sleeve encircles the castable sleeve and expands to conform to the inner dimensions of a particular MRI coil or CT scanner.
Alternatively, the apparatus includes a castable sleeve that conforms via the castable material to both the limb of the patient and the inner dimension of a particular MRI coil or CT scanner.
Alternatively, the apparatus includes a castable sleeve for casting around a flex/wrap or surface coil. In one embodiment, the surface coil is wrapped around the limb of a patient and the castable sleeve is positioned over the surface coil or the castable sleeve is integrated into the surface coil to ensure rigid fixation and custom fit of the coil between the limb and the coil, as well as the coil and the MRI scanner.